Stabilized compositions containing hydrogenated quinolines with oxidation inhibitors



Patented Aug. 4, 1953 STABILIZED COMPOSITIONS CONTAINING HYDROGENATEDQUINOLINES WITH OXI- DATION INHIBITORS Allen R. Jones, Roselle, and John0. Smith, Jr., North Plainfield, N. J., assignors to Standard OilDevelopment Company, a corporation of Delaware No Drawing. ApplicationJanuary 26, 1949, Serial No. 72,993

5 Claims.

This invention relates to an improved class of oxidation inhibitorsconsisting of hydrogenated quinolines. The invention also concerns animproved combination of oxidation inhibitors consisting of a mixture ofhydrogenated quinolines and conventional types of oxidation inhibitors.In accordance with this invention, an oxidation unstable material, suchas gasoline or lubricating oil, may be inhibited against deteriorationnormally caused by oxidation, by incorporating therein small quantitiesof the oxidation inhibitors of this invention. The invention also hasparticular application to the stabilization of lead antiknock compoundsto prevent the precipitation of these lead compounds in concentratedlead fluids or in gasoline compositions containing these lead antiknockcompounds.

In the petroleum industry, it is generally desirable in order to preparea superior quality of gasoline or lubricant, to stabilize thesematerials against degradation caused by oxidation. In general,hydrocarbon mixtures falling in the gasoline or lubricating oil boilingrange, if unstabilized, will, over a period of time, be subject to gumformation, sludge formation, the formation of acids or objectionablecolor bodies. Furthermore, if lead antiknock agents are incorporated inthe hydrocarbon mixture, it is generally desirable to stabilize the leadcompounds against precipitation. At the present time, therefore, it isgenerally the practice to incorporate in a lubricating oil, a gasoline,or similar hydrocarbon mixture, a suitable agent which will inhibitoxidation of these mixtures. These agents are generally called oxidationinhibitors or antioxidants and presently consist of compounds selectedfrom the classes consisting of amines or phenols. For example, suitableoxidation inhibitors known to the art consist of a-naphthol,,B-naphthol, mixed xylenols, 2,4-di-tert.-butyl-4-methyl phenol, hydroquinone, aniline, a-naphthylamine, phenyl-B- naphthylamine,N,N'-di-sec.-butyl-p-phenylene diamine, diphenyl p-phenylene diamine,N,nbutyl-p-aminophenol and 2,4-diamine phenol. While all of the aboveindicated inhibitors are more or less successful in reducing theinstability of hydrocarbon mixtures, none of the inhibitors is effectivein actually preventing all degradation indefinitely. Thus, while thedegree of stability afforded by each of the above inhibitors variessomewhat, each of the inhibitors is only successful in partiallystabilizing hydrocarbon mixtures over a period of time. It is,therefore, the principal object of this invention to provide an improvedtype of oxidation inhibitor which will more effectively stabilizehydrocarbon mixtures against oxidation.

The discovery on which this invention is based is that the hydrogenatedquinolines as a class have remarkable oxidation inhibiting properties.Thus hydrogenated quinolines may be employed by themselves as inhibitorswith beneficial results. More basically, however, it has been discoveredthat hydrogenated quinolines in some manner act with conventional typesof antioxidants to provide a synergistic effect remarkably enhancing theantioxidant properties of these compounds. In accordance with thisinvention, therefore, hydrogenated quinolines may be used by themselvesor preferably in combination with conventional inhibitors of the classesindicated above to provide oxidation inhibitors of improvedeffectiveness.

While, as indicated, it is contemplated that hydrogenated quinolines maybeneficially be employed in combination with any of the conventionalantioxidants, the preferred combination is the combination of ahydrogenated quinoline and an amino phenol. Of the alkyl phenols, thetri alkyl phenols and specifically the 2,4,6 tri alkyl phenols arepreferred. Still more specifically, 2,4,6 tri alkyl phenols having atertiary butyl group in either or both of the 2 and 6 positions eitherwith or Without a normal alkyl group of 1-4 carbon atoms in the 4positions may be employed. Similarly in the case of diamine typeinhibitors, the para phenylenediamine inhibitors are preferred andparticularly para phenylenediamine inhibitors having alkyl groups of 3-5carbon atoms on the amino groups. Again in the case of amino phenolinhibitors, 3-5 carbon atom alkyl groups may be positioned on thenitrogen atom. As will be disclosed, it now appears that a hydrogenatedquinoline may be used in combination with any of these inhibitors toprovide a synergistic antioxidant effect.

The hydrogenated quinolines which may be employed in the practice ofthis invention are generally any compound derived from the hydrogenationor reduction of quinoline or substituted quinoline. The class ofcompounds within the scope of this invention comprises quinolines havingeither the heterocyclic ring or both the heterocyclic and benzene ringsof the compound saturated with hydrogen, for example, 1,23,4-tetrahydroquinoline and decahydroquinaldine. This class of compoundsalso consists of the hydrogenated quinolines just described which havealkyl, cycloparaffinic, or aryl groups attached to either theheterocyclic or benzene nucleus. Specific compounds falling within thescope of this invention are: 1,2,3,4-tetrahydroquinoline, 1,2,3,4-tetrahydroquinaldine, decahydroquinoline and decahydroquinaldine. Asstated above, any of these compounds may be utilized by itself orcombinations of these compounds may be employed as oxidation inhibitors.However, it is preferred that any one or any combination of the abovecompounds be employed with one or more of the conventional oxidationinhibitors formerly indicated falling in the broad classes of amines orphenols.

The total amount of antioxident to be employed in a given applicationmay generally be stated to be that amount employed according to currentpractices. This amount varies widely depending upon the particularapplication of the antioxidant. For example, in the stabilization ofgasolines, in general, about one half to ten pounds per 5000 gallons ofinhibitor are employed to prevent gum formation during the storage ofthe gasoline. Again in the case of the stabilization of lubricatingoils, up to several per cent of antioxidant may be employed in order toprevent the formation of sludge, varnish or acidic materials during theservice life of the lubricant. Similarly, in the application ofantioxidants to stabilize concentrated mixtures of lead antiknock agentsagainst precipitation, about 0.05 to 1.0 per cent of antioxidant may beemployed. It is apparent that the above indicated ranges of antioxidantto be employed in any particular application may be varied as desiredand it is furthermore apparent that many other applications ofantioxidants may be made within and without the petroleum industry.Thus, it is contemplated that the oxidation inhibitors of this inventionmay be employed to stabilize synthetic or natural rubber, plastics,greases, waxes, edible fats and oils, etc. Any proportional combinationof inhibitors may be employed according to the broad concept of thisinvention. In general, it is contemplated that mixtures of anyhydrogenated quinoline and conventional antioxidants may be used inwhich the ratio of the hydrogenated quinoline to conventionalantioxidant falls substantially within the range of 0.1 to by weight.However, it is preferred that in order to obtain the optimum synergisticefiect provided by the unique combination of antioxidants, that thehydrogenated quinoline should be used in approximately equal proportionswith the conventional antioxidant for most applications.

The nature of this invention will be more fully understood from aconsideration ofthe following examples embodying the principles of thisinvention.

As an example of this invention, a turbine oil was tested for stabilitywithout any oxidation inhibitors, with a conventional phenolicinhibitor, with a hydrogenated quinoline, and with combinations of thehydrogenated quinoline and the phenolic inhibitor. The turbine oiltested was a petroleum neutral oil having a viscosity of about &3Saybolt seconds at 210 F. and containing 0.06

weight per cent of zinc naphthenate as a co1" rosion inhibitor. Thestability of this oil alone and with the addition of the above additiveswas determined by means of a modified Staeger test. In this test asample of the oil is placed in a beaker with a polished copper strip andmaintained at a temperature of C. during the test period in an ovenequipped with a rotating shelf. The performance of the oil is determinedby measuring the time for the neutralization number of the sample toincrease by 0.20 mg. KOH/ gram over the neutralization number of theoriginal sample at the start of the test. This value is determined byperiodically extracting samples from the beaker container in the ovenand the value obtained is ordinarily designated as the Staeger life. Theresults of the indicated test are presented in Table I.

TABLE I Modified Staeger test for turbine oils [Petroleum neutral oil+0.06 wt. percent zinc napthenete] 1 Time to reach an increase inneutralization number over original sample of 0.20 mg. KOH/g.

It will be noted from this table that the turbine oil tests, when theoil contained no oxidation inhibitor, had a Staeger life of 72 hours. Byincorporating 0.4 weight per cent of the conventional inhibitor,2,6-di-t-butyl-4-methyl phenol, in the turbine oil, the Staeger life wasincreased to 445 hours. Similarly, when incorporating 0.4 weight percent of 1,2,3,4-tetrahydroquinoline in the oil, the Staeger life Wasfound to be 315 hours. Finally, in the last line of the table, whenemploying 0.2 weight per cent of each of the above indicated inhibitors,it was found that the Staeger life was 520 hours. It will be noted thatthe stability of the oil indicated by these tests was unexpectedlygreater when 50/50 proportions of the two inhibitors were employed overthe case when the same total amount of either of the inhibitors wasused.

As a further example of this invention, several hydrogenated quinolineswere evaluated alone and with a conventional gasoline antioxidant in anuninhibited motor fuel. The oxidation stability of the gasoline wasdetermined by means of the ASTM induction period method which isnormally used for determining the oxidation stability of gasolines. TheASTM test designation is D 525-46. The gasoline employed in the testconstituted a commercial blend of thermally cracked stock, catalyticallycracked stock and straight run gasoline distillate containing about 1ml. of tetraethyl lead per gallon. The conventional oxidation inhibitoremployed in these experiments, identified in Table II as Antioxidant,was N,N'-di-sec. butyl-para-phenylenediamine. The hydrogenatedquinolines employed, identified in Table II as Synergist, weretetrahydroquinoline, decahydroquinoline, tetrahydroquinaldine and amixture of hydroquinaldines consisting of about 60% tetrahydroquinal-TABLE 'II ASTM oxidation test results Antioxidant Concentration, 'lb. /5,000 gaL o 5 5 Synergist Concentration, lb $5,000 gaL i 10 '0 5Synergist Induction Period, MinJ 6 None; 825 l Tetrahydroquinoline 140 845 l, 240 I 855 Decahydroquino'line '75 845 1,175 2 =320Tetrahydroquinaldine- -1 10 845 .995 125 Mixed Hydroquinaldines B 130 p845 960 80 Approximately 60% tetrahydroqii'inaldine and 40%'decahydroq'uinaldine.

- Average of two or more determinations. I V

Y Increase ininduction'period over base gasoline due to combination ofadditives (l0 lbs/5,000 gals.) minus the sum of the induction periodincrease due to eachadditive lbs./5,000 gals.)

It will be noted that the antioxidant effect of the combination of theconventional antioxidant and any of the hydrogenated quinolines wasappreciably greater than that which would 'be expected based upon theantioxidant activity of the hydrogenated quinolines alone or theconventional antioxidant alone. It has been found convenient to expressthe synergistic activity of the hydrogenated 'quinolines as the increasein induction period over that of the base gasoline due to the.combination of additives minus the sum of the induction period increasedue to each of the component additives. As an example, considering theeffect of the tetrahydroquinolin'e: the uninhibited gasoline had aninduction period of 60 minutes while the gasoline containing lbs/5000gals. of tetrahydroquinoline had an induction period of 140' minutes,indicating an increase in induction period of about minutes for 5lbs/5000 gals. of the tetrahydroquinoline. Similarly the increase ininduction period due to 5 lbs/5000 gals. ofN,N-di-sec.butyl-paraphenylenediamine was 785 minutes while the increasedue to 5 lbs. of both of the additives was 1180 minutes. The net gain ininduction period due to the synergistic combination of these additiveswas therefore 1180(785+40) or about 355 minutes. Thus, it may be seenfrom the table above that there is a net gain in the ASTM inductionperiod of 80 to 355 minutes when the 1 combination of a hydrogenatedquinoline and N,N-di-sec.-butyl-p-phenylenediamine is employed. It isparticularly notable that each of the four hydrogenated quinolinesamples tested exhibited this synergistic eliect with this conventionalgasoline antioxidant.

A further evaluation of the synergistic antioxidant activity ofhydrogenated quinolines was made employing a gasoline similar to thatdescribed in the preceding example. In this example other conventionalgasoline antioxidants of the amino phenol and trialkyl phenol classeswere employed. The particular compounds employed weretetrahydroquinoline and tetrahydroquinaldine as examples of hydrogenatedquinolines, and N-n-butyl-p-aminophenol and 2,6-ditertiarybutyl--methylphenol, which are examples of the classes of conventionalantioxidants formerly identified.

ASTM o'middtzh'iz test results methyl phenol Antioxidant Concentration:

1b. l 0 2:5 Synergis't Concentration:

Net; Induction I sjynergist Period- '1 Average of two determinations. V

Increase'ininductiou per'iodove'r'basegasoline due to combinationoi-additives -(5 lbs/5,000 gals.) minus the sum of the induction periodincreasc due to-each additive (2;-5lbs.'/5,000'gals;). Thus, .it isapparent from Table III above that with both of these .conventionalgasoline antioxidants in combination with each of the hydrogenatedquinolines, a synergistic efiect was observed which resulted-in anet-gain in the ASTM induction period.

As one further example of this invention, the oxidation inhibitors-ofthis invention were tested in a somewhat diiferent application. In thisexample, .a concentrated lead fluid was employed consisting of onetheory of ethylene dibromide and .pure tetraethyl lead. Qne theory-ofethylene dibromide identifies the amount of dibromide required to dormlead bromide in .stoichiometric proportions. This mixture of tetra ethyllead and ethylene :dibrom-ide is very similar to the mixture normallyemployed in aviation gasolines. Normally this mixture .-is characterizedby a tendency for lead precipitation .during storage :of sufiicientmagnitude to cause severe diiiiculties in engine operation after longperiods of storage, particularly in hot climates. This precipitation mayoccur either with the concentrated lead mix or with leaded gasolines.While the mechanism of the lead decomposition is not thoroughlyunderstood, it appears that the lead precipitation may be initiated byoxidation. In any case, it has been established that lead precipitationcan be substantially minimized by employing a suitable antioxidanteither to prevent precipitation in the concentrated lead fluid or in thegasoline containing lead. In order to demonstrate the inhibiting actionOf a hydrogenated quinoline-conventional antioxidant combination forpreventing the undesirable lead precipitation just described, samples ofa mixture of pure tetraethyl lead and pure ethylene dibromide werestored with a steel strip in brown glass bottles kept in a bathmaintained at a constant temperature of F. The samples that were storedincluded one to which no antioxidant had been added, one in which 0.1weight percent of tetrahydroquinaldine Was added, one which contained0.1 weight percent of 2,6-di-tertiary-butyl-4- methyl-phenol, and onecontaining 0.05 weight percent each of the hydrogenated quinoline andthe phenol. The extent of degradation of the tetraethyl lead fluid wasdetermined by periodically examining the samples and visually estimatingthe amount of lead precipitation present. It has been found convenientto express the stability of the various samples as the time in days required to reach a. precipitation level arbitrarily chosen as moderate.The results of the test just described are shown in the following table.

TABLE IV Storage tests of tetraethyl lead fluid at 120 F.

[Brown bott1esSteel strip.]

1 Commercial grade of antiknock agent containing tetra.

ethyl-lead and one theory or molar-equivalent of ethylene dibromide. vThus it can be seen that the time required to reach the moderateprecipitation level is greatly extended by the use of eithertetrahydroquinaldine or 2,6-di-tertiary-butyll-methyl phenol. Thecombination of these two additives added to the lead mix in the sametotal concentration even more remarkedly improved the stability of thelead mixture. Thus the synergistic activity of a hydrogenated quinolinewhen employed with a trialkyl phenol is clearly demonstrated in thisapplication of retarding lead precipitation.

What is claimed is:

1. A hydrocarbon composition normally characterized by oxidationinstability containing small quantities of a hydrogenated quinolineselected from the class consisting of tetrahydroquinoline,tetrahydroquinaldine, decahydroquinoline, and decahydroquinaldine and anoxidation inhibitor consisting of N-n-butyl paramino phenol, saidcomposition containing a weight ratio of said hydrogenated quoline tosaid inhibitor ranging from 0.1 to 10.

2. A hydrocarbon composition normally characterized by oxidationinstability containing small quantities of a hydrogenated quinol'ineSe"- lected from the class consisting of tetrahydroquinoline,tetrahydroquinaldine, decahydroquinoline, and decahydroquinaldine insynergistic combination with an oxidation inhibitor compound selectedfrom the group consisting of N-nbutyl para-amino phenol,N-N'-di-secondary butyl para-phenylene diamine and 2,6-di-tertiarybutyll-methyl phenol, said composition containing a weight ratio ofhydrogenated quinoline to inhibitor ranging from 0.1 to 10.

3. -A hydrocarbon composition normally characterized by oxidationinstability containing small quantities of a hydrogenated quinolineselected from the class consisting of tetrahydroquinoline andtetrahydroquinaldine and an oxidation inhibitor selected from the classconsisting of N-n-butyl para-amino phenol, N-N-disecondary butylpara-phenylene diamine and 2,6- di-tertiary butyl-4-methyl phenol, saidcomposition containing a weight ratio of said hydrogenated quinoline tosaid inhibitor ranging from 0.1 to 10.

4. A composition according to claim 3 in which the hydrocarboncomposition is gasoline and in which the total weight percentage of thehydrogenated quinoline and the inhibitor is about 0.05

p to 25 pounds per 1,000 gallons of gasoline.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,030,033 McConnell Feb. 4, 1936 2,363,778 Pedersen Nov. 28,1944 2,387,751 Dickey et a1. Oct. 30, 1945 2,512,297 Biswell et a1 June20, 1950

1. A HYDROCARBON COMPOSITION NORMALLY CHARACTERIZED BY OXIDATIONINSTABILITY CONTAINING SMALL QUANTITIES OF A HYDROGENATED QUINOLINESELECTED FROM THE CALSS CONSISTING OF TETRAHYDROQUINOLINE,TETRAHYDROQUINALDINE, DECAHYDROQUINOLINE, AND DECAHYDROQUINALDINE AND ANOXIDATION INHIBITOR CONSISTING OF N-NBUTYL PARAMINO PHENOL, SAIDCOMPOSITION CONTAINING A WEIGHT RATIO OF SAID HYDROGENATED QUOLINE TOSAID INHIBITOR RANGING FROM 0.1 TO 10.